Among conventional rotational speed detection devices is, for example, a number-of-revolutions measurement device described in Patent Document 1 that includes a rotator, an image capture element that captures an image of a mark attached to the rotator, and an image processing unit that processes the image captured by the image capture element, and is configured to detect the rotation of the rotator mark using the image processing unit and thereby measure the number of revolutions of the rotator. In addition to the measurement of the number of revolutions of the rotor using the image capture element, Patent Document 1 also describes an alternative technique of measuring the number of revolutions by emitting laser to a rotator and then optically measuring a change in pattern of reflection or interference caused by rotation.
Patent Document 2 also describes a similar number-of-revolutions measurement device that includes a rotator, a CCD camera that captures an image of a mark attached to the rotator, and an image processing unit that processes the image captured by the CCD camera, and measures the number of revolutions of the rotator by detecting the rotator mark using the image processing unit. Patent Document 2 also states that a light emitting unit that emits laser light to the rotator and a light receiving unit that receives the laser light reflected by the rotator are provided, and the number of revolutions is detected by detecting a change in pattern of reflection or interference caused by the rotation of the rotator using a number-of-revolutions detection unit.